1. Field of the Invention
The present invention relates to a control method/system for controlling upshifting in an at least partially automated mechanical transmission system. In particular, the present invention, in one preferred embodiment, relates to the control of upshifting in a vehicular automated mechanical transmission system wherein the system senses conditions indicative of a requirement for an upshift from a currently engaged gear ratio (GR) and evaluates, in sequence, the desirability of unaided upshifts and then upshift brake-assisted upshifts and commands upshifts deemed desirable.
More particularly, the present invention relates to a control method/system for controlling upshift brakes in potential upshift brake-aided upshifts as a function of one or more of the thermal characteristics of the upshift brake, the estimated current temperature of the brake, the period of time since the previous upshift brake-aided upshift and/or the expected heat energy generated by the previous upshift brake-aided upshift and/or the by the upshift under consideration at differing levels of brake caused retardation.
2. Description of the Prior Art
Fully or partially automated mechanical transmission systems for vehicular use are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,648,290; 4,722,248; 4,850,236; 5,389,053; 5,487,004; 5,435,212 and 5,755,639, the disclosures of which are incorporated herein by reference. The use of engine brakes (also known as compression brakes, exhaust brakes or Jake brakes) and transmission controls utilizing same are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 5,409,432 and 5,425,689, the disclosures of which are incorporated herein by reference.
The use of friction devices to retard transmission input shaft rotation, such as inertia brakes (also known as upshift brakes or input shaft brakes) and actuators therefor, for providing quicker upshifts is known in the prior art, as may be seen by reference to U.S. Pat. Nos. 5,086,659 and 5,713,445, the disclosures of which are incorporated herein by reference.
Controls for automated mechanical transmission systems, especially wherein shifting is accomplished while maintaining the master clutch engaged, wherein single and/or skip shift feasibility is evaluated are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,576,065; 4,916,979; 5,335,566; 5,425,689; 5,272,939; 5,479,345; 5,533,946; 5,582,069; 5,620,392; 5,489,247; 5,490,063; 5,509,867, and 6,149,545, the disclosures of which are incorporated herein by reference.
Controls for automated mechanical transmission systems including control of friction upshift brakes are known in the prior art as may be seen by reference to U.S. Pat. No. 6,123,643, the disclosure of which is incorporated herein by reference.
In the system described in U.S. Pat. No. 6,149,545, a control for a vehicular automated mechanical transmission system will sense conditions indicative of upshifting from a currently engaged gear ratio, will evaluate, in sequence, the desirability of large skip upshifts, then single skip upshifts, unaided single upshifts and then upshift brake-aided single upshifts, and will command an upshift to the first target ratio deemed to be feasible under current vehicle operating conditions.
The upshift feasibility rules comprise a two-part test, (a) can the upshift be completed above a minimum engine speed? and (b) when completed, will the engine, in the target ratio, provide sufficient torque at the drive wheels to allow at least a minimum vehicle acceleration? Feasibility of skip and/or single upshifts also may require that an upshift is expected to be completed within a period of time less than a maximum acceptable time (T less than TMAX?).
The control of the present invention relates to controlling a friction upshift brake which may be operated at two or more levels of retardation to provide variable additional deceleration, during a shift with the master clutch engaged, to a transmission input shift and the engine crank shaft and master clutch rotating therewith. This retardation is additive to the natural rate of deceleration of the engine called xe2x80x9cengine speed decayxe2x80x9d due to friction and the like. Actuation of the upshift brake will apply an added retarding force to the input shaft, clutch and, engine assembly to provide an additional deceleration of the input shaft.
To prevent undue wear and/or damage of friction-type upshift brakes, the predicted maximum deceleration available from the upshift brake without causing the brake to overheat (TEMPp less than TEMPMAX) is estimated or simulated. This maximum deceleration is then compared to the deceleration necessary to complete a potential downshift.
If the additional deceleration needed to complete a shift above a minimal engine speed and/or within a maximum acceptable time exceeds the maximum additional deceleration the upshift brake can provide without damage, usually thermal damage, an upshift into the target gear is not commanded.
If an upshift is feasible, the upshift brake will be utilized to provide a degree of deceleration to allow the shift to occur above the minimum engine speed, and, if possible, within a desirable period of time (such as, for example, within 1.2 seconds for a heavy-duty truck).
Accordingly, an improved upshift control for automated mechanical transmissions is provided which will automatically evaluate and command an acceptable level of upshift brake actuation for a proposed upshift brake-aided upshifts and which provides thermal protection for the friction-type upshift brake.
This and other objects and advantages of the present invention will become apparent from a reading of the following description of the preferred embodiment taken in connection with the attached drawings.